1. Field of the Invention
The present invention relates to a method to manufacture an optical module, in particular, the method according to the present invention relates to manufacture an optical module implementing with, what is called, a pig-tailed arrangement and an arrangement of the optical module.
2. Related Prior Art
An optical module applicable to the optical communication system generally comprises a housing that installs a semiconductor optical device such as a semiconductor light-emitting device and a coupling mechanism to couple to a pig-tailed optical fiber with the optical device. The process to align the pig-tailed fiber with the housing, in particular, to assemble the coupling member with the housing generally applies, what is called, the YAG laser welding. However, the YAG laser welding often causes the misalignment between the coupling member and the housing, where they are optically aligned once in advance to the YAG laser welding, which causes substantial optical loss between the pig-tailed fiber and the semiconductor light emitting device. Various techniques have been proposed to compensate the misalignment by the YAG laser welding.
FIG. 2 is a cross section of an optical module taken along the optical axis of the ferrule 14 and explains the mechanism to cause the misalignment after the YAG laser welding. A conventional process to assemble the ferrule 14 with the ferrule holder 13 is such that: the piercing welding for the ferule 14 by the YAG laser beam is firstly performed for the ferrule holder 13 at a longitudinal center X12 thereof; then, the fillet welding also by the YAG laser beam is carried out for the end X13 of the ferrule holder 13. Subsequently, the assembly of the ferrule 14 with the ferrule holder 13 is optically aligned with the optical device 12 as sliding the ferrule holder 13 on the end surface of the window holder 11a and fixed thereto by the fillet welding by using the YAG laser beam at the position X11. The YAG laser welding for the points, X11 to X13, are generally done for a plurality points each radially distributed with an equal angle.
However, the fillet welding at the position X11 sometimes causes the misalignment between the assembly, 13 and 14, and the optical device 12, which are optically aligned once in advance to the fillet welding. Moreover, when the optical coupling between the optical device 12 with the pig-tailed fiber 15 is insufficient compared with the preset value after the fillet welding at the point X11, some additional welding will be necessary to be carried out.
One technique to recover the optical coupling has been known, where a point just between the points, to which the prior welding, X11 to X13, are carried out, is first irradiated by the YAG laser beam as rotating the optical module 10 around the optical axis. When the optical coupling recovers the preset value, the process to assemble the optical module 10 is completed. When the optical coupling improves but the practical value is still insufficient for the preset value, an additional welding will be iterated as slightly rotating the optical module 10 from the current position until the preset value will be obtained.
On the other hand, when the optical coupling after the first slight rotation degrades from a former value, which means that the rotation angle done before the additional welding is reverse, the optical module 10 recovers the position of the first one point welding, then the optical module is slightly rotated in a reverse angle and carried out the one point welding.
When the first one point welding after the rotation of the optical module 10 degrades the optical coupling efficiency, which means that the first rotation is incorrect, the optical module 10 will be rotated by 180° from the position of the first one point welding and iterated the procedures of the slight rotation and the one point welding until the preset value for the optical coupling will be obtained. Thus, the conventional method to recover the optical coupling efficiency iterates the step of the one point welding as slightly rotating the optical module. However, when the iterating welding continues, the ferrule holder 13 sometimes leaves no space to be welded to the ferrule 14, or, the iterated number of the welding results in a rigid fixation of the ferrule holder 14 with the ferrule such that no improvement in the optical coupling efficiency is obtained in the following welding.